I am one Atheist who is absolutely not involved in any kind of war on Christmas. I personally enjoy the holiday season very much and am very involved in spreading holiday joy!
Why do I love Christmas even though I consider myself a militant atheist? Most of all, I'd say it's because the glow of loving all humans is such a great feeling, and around the holiday season there seems to be so much of this. I do my part to get and give that glow at all times of the year. It seems like such a waste when people are only giving and loving during the holidays.
I don't really believe the war on Christmas exists. Even if it did, we would never be able to win the battle; it would be as futile as the war on drugs. I think certain religious groups, who somehow feel threatened by the idea that there may be other notions of the holidays or what they mean, have invented the war on Christmas as part of their great persecution myth.